Selecting Heads - Piston to Valve Clearance?

[Sgt.5point0]

I'm going to be getting a set of heads within the next two months and I'm kinda curious as to what valve size I can use with my stock 1993 pistons.

I was looking at the TFS Twisted Wedge Track Heat but they have 2.02 and 1.60 valves. Now I realize that changing the cam or putting in 1.7 rockers or both will affect the clearance.

So how do you figure out if you're go/no-go on the clearance?



ps... Only heads I've come across with 1.90/1.60 valves are the Roush 160s and the Edelbrock Performer RPM... so that kinda cuts down the selection process if 2.02's won't work for me.

 

[Michael Yount]

AFR 165's have 1.90/1.60's; FRPP X and Y heads have 1.94/1.54 valves. There are many very impressive combos out there with the AFR's and off the shelf as well as custom cams. So you'll have plenty to choose from. Others will be able to give you some idea of what combinations will clear, but once you've decided, you must measure your combo to see what the clearances are - there's no way around that. Others can tell you their clearance, but even if the parts are the same, tolerances measured that closely always vary from engine to engine. You're correct that cam and valve size will impact clearance; your rocker ratio will have only a very minimal (almost negligible) impact on clearance. The best approach is to deal with a reputable supplier on the components so that if you do have a clearance issue, you can, for example, return the cam for one with a bit less duration that will clear. Central Coast Mustang worked with me that way - actually sending me two cams and letting me use the one that cleared, and returning the other one (which they then credited my account for). And, of course, you can just have the stock reliefs cut a bit larger - that takes care of the issue as well. Near as I can tell, for valves in the 1.90-1.94/1.60-1.54 range, cams with duration less than 220 intake/226 exhaust should have enough clearance with the stock 93 pistons. Just Monday night we measured stock E7 valves and a TFS II cam (224/232 I think) on a flat top 86 block (less clearance) - and it had less than acceptable minimum clearance on the exhaust, and the intake would've actually had the valves hitting the pistons. I pass that info along ONLY to give you some idea of how to start asking questions. You have to measure the clearance for certainty once you've decided on components - there's simply no substitute for that unless you're willing to risk damage based on yours or someone else's guess. You're looking for a minimum of .080" on intake and .100" on exhaust. Good luck with your choices.

 

[Sgt.5point0]

Thanks Mike, I really do appreciate you taking the time to answer my question.

I have another question though now, lol. What is involved in making the stock reliefs larger? Is that something that a guy can do in his garage or do you have to take your car into a machine shop. I was kinda planning on doing the head swap with my brother in his garage.

Also if I'm not mistaken the reliefs have to be moved for Twisted Wedge heads, right?

 

[Mike86Stang]

Well I used a Isky Piston Notching Tool & Notched all my pistons in my mothers garage

 

[Michael Yount]

Yeah - what MSTANG said - it can be done at home. And yes, I believe the configuration with the TFS heads is slightly different; an alternative would be the AFR185's - same bigger valves, but they're configured in the same location as the stock reliefs/valves. PM MSTANG for more info on the Isky relief cutting tool. Or you can pull the pistons/rods and take them to a machine shop and have it done.